The present invention relates generally to electrical stimulators for biological tissue and more particularly to electrical stimulators for biological tissue having mode control.
Electrical stimulators providing an electrical stimulus signal are useful for biological tissue. One significant use for electrical stimulators of this type is for transcutaneous electrical nerve stimulation (TENS) which generate carefully controlled electrical stimulus parameter signals which are delivered via suitable electrodes through a patients' skin to underlying biological tissue. The electrical stimulus signals may be utilized for the purpose of masking pain signals, for example, the sensation of pain felt by a patient after surgery. Because the patient's response to transcutaneous electrical nerve stimulation may vary significantly, a wide range of electrical stimulus signals must be provided. A second use of electrical stimulators is for neuromuscular stimulation (NMS) in order to initiate or control muscular contraction in a patient. Since a wide variety of muscular actions are available again a wide variety of electrical stimulus signals must be provided.
Electrical stimulators may deliver an electrical stimulus signal, which is to be applied to biological tissue, of a pulsatile nature. The pulsatile signal has a pulse amplitude, a pulse duration and a pulse frequency. The electrical stimulus signal may be varied from predetermined stimulus parameter values according to a predetermined criteria. One means to vary such stimulus parameters is to specify maximum values for pulse amplitude, pulse duration and/or pulse frequency or repetition rate. These maximum values may then be individually varied according to known criteria (such as random variation between a minimum value and a maximum value). The pulse amplitude may be varied from 100% of the specified maximum value to 60% of the specified maximum value on a random basis. Simultaneously the pulse duration may be separately, or simultaneous but independently, varied from 100% of the specified maximum value to 40% of specified maximum value on a random basis. Thus, while the maximum (or other predetermined) value of the electrical stimulus parameters are specified the actual pulses output by the electrical stimulator are likely to be only fractions of the specified maximum electrical stimulus parameter values. Such a variation of electrical stimulus parameters leads to difficulty in setting or adjusting the maximum values to an individual patients' need or comfort.